Primary Failure of Eruption: A Diagnosis of Exclusion

Eruption is the process whereby a tooth moves from its crypt position, through the alveolar process and into the oral cavity. Significant deviation in the expected eruption time is not an uncommon finding in clinical practice. Suspicion should be raised if teeth fail to erupt within 2 years of the expected eruption date, or if eruption is delayed by over 6 months compared to the contralateral tooth.¹ There are many reasons why eruption may be delayed and, in some cases, teeth can completely fail to erupt.

Primary failure of eruption (PFE) is a rare condition, characterized by non-syndromic, partial or complete non-eruption of a tooth or several teeth, despite a clear eruption pathway.² This occurs due to a malfunction in the tooth's eruptive mechanism. Affected teeth have an abnormal and limited response to orthodontic forces, and can become ankylosed when orthodontic forces are applied.²

Diagnosis of PFE is a process of exclusion once all other causative factors have been considered and eliminated.³ Early identification can help mitigate potential adverse effects and facilitate early treatment planning. This article describes the aetiology, clinical presentation and management of PFE, as well as describing other causes of delayed and failed eruption that should be considered as differential diagnoses.

Causes of delayed and failed tooth eruption

Numerous local and systemic factors have been linked with delayed and failed tooth eruption. Local causes are the most common and include impaction due to supernumerary teeth, mucosal barriers, scar tissue and tumours (Table 1). Systemic and syndromic causes usually affect multiple teeth (Table 2).

Local causes of delayed tooth eruption

Impaction

Teeth may fail to erupt normally owing to the presence of supernumerary teeth, odontomas, cysts, tumours and morphological abnormalities, such as crown or root dilacerations and enamel pearls (Figure 1). This can usually be confirmed following plain film radiography or cone beam computed tomography (CBCT). Treatment involves removing the cause of the impaction, with or without tooth exposure and orthodontic traction.

Ectopic tooth germ position

Ectopic teeth are in an atypical position or orientation (Figure 2). This can lead to a delay or complete failure of the tooth to erupt. This is often due to an arch length deficiency and subsequent crowding. It most frequently affects the maxillary arch, and the most commonly affected teeth are first permanent molars and canines.⁷

Mucosal barriers

Fibrous or thick gingival tissue may delay tooth eruption. This might result from previous trauma or surgical intervention. Gingival overgrowth, which can be drug induced or hereditary, such as hereditary gingival fibrous hyperplasia, can also disturb tooth eruption. A simple incision usually releases the crown allowing the tooth to erupt spontaneously.

Long-term sequelae of radiotherapy

Children who have received radiotherapy to the head and neck are at increased risk of abnormal dental development. These abnormalities include tooth agenesis, abnormal tooth development and delayed eruption.⁸ Abnormalities are generally more severe in children who received radiation at an earlier stage in their development and at higher doses.

Regional odontodysplasia

Regional odontodysplasia is a rare developmental anomaly affecting the enamel, dentine and cementum (Figure 3). Teeth in a particular region or quadrant are affected. Clinical features include short roots, open apical foramina and large pulp chambers. Tooth eruption is either delayed or completely fails to occur.⁹

Systemic causes of delayed tooth eruption

Endocrine disorders

Hypothyroidism, hypopituitarism and hypoparathyroidism have all been linked with eruption delays.¹⁰ This can manifest as the retention of primary teeth, impaired upper and lower jaw growth with subsequent alterations in facial dimensions.¹¹

Premature birth

Prematurity and low-birth weight have been linked to delayed tooth eruption. Aktoren et al found that babies weighing less than 2.5 kg at birth had an eruption delay of approximately 2 months compared to children weighing more than 2.5 kg.¹²

Malnutrition

Chronic and prolonged malnutrition during infancy have been linked to delays in eruption. Deficiencies in vitamins A and D are the most common causes of delayed eruption in the permanent dentition. Delays ranging from 1 to 4 months have been reported.¹⁰

Drug treatments

Many drug treatments, for example long-term chemotherapy, or drugs inhibiting prostaglandin pathways such as aspirin, acetaminophen and ibuprofen, can slow the rate of tooth eruption by decreasing osteoclastic activity in periodontal tissues.¹⁰ Similarly, bisphosphonate drugs have also been linked to eruption delays.¹³ In addition to this, drugs inducing gingival overgrowth, such as anticonvulsants (e.g. phenytoin, sodium valproate), immunosuppressants (e.g. ciclosporin) and calcium channel blockers (e.g. nifedipine, verapamil) may also cause delayed tooth eruption owing to increased thickening of the mucosa.¹⁴

Syndromes

Many syndromes including cleidocranial dysplasia, Down syndrome and ectodermal dysplasia are associated with delays and failure of eruption of both dentitions. These are summarized in Table 2. Figure 4 shows a 10-year-old child diagnosed with cleidocranial dysplasia.

Primary failure of eruption

PFE is a rare dental anomaly first described by Proffit and Vig in 1981.² The condition is characterized by partial or complete failure of a tooth to erupt into occlusion, which is believed to be due to a malfunction in the tooth's eruptive mechanism. PFE has a prevalence of 0.06%, with a slight female predilection.¹⁵ Teeth may initially erupt into occlusion, but then cease to erupt any further, or may fail to erupt completely.

PFE almost entirely affects posterior teeth and can affect both the primary and permanent dentitions, which can lead to a severe posterior open bite with associated impaired growth of the alveolar process. Usually, all teeth distal to the most mesially affected tooth exhibit the disorder.¹⁶ A systematic review by Ahmad et al found that 45% of affected teeth completely fail to erupt, whereas 55% will partially erupt, suggesting that the eruption malfunction can occur at different stages in the eruption process.¹⁷ The clinical features of PFE are summarized in Table 3.

Figure 5 shows a 10-year-old child with primary failure of eruption of the upper left first permanent molar. Asymmetry in the developing dentition should raise concern and warrant further investigation. In this case, three first permanent molars had fully erupted and upper left first permanent molar had failed to erupt, which prompted the clinician to undertake a dental panoramic tomograph (DPT) and refer the patient for specialist treatment planning. Further cases of PFE are shown in Figures 6 and 7.

Types of PFE

Three types of PFE have been described in the literature:

• Type 1: all affected teeth exhibit a similar lack of eruption potential, with a progressive open bite from anterior to posterior.¹⁸ Failure in the eruptive mechanism is believed to occur at a particular point in time (Figure 8a).¹⁹
• Type 2: tooth/teeth distal to the most mesially affected tooth exhibit greater, albeit inadequate, eruption.¹⁸ Failure in the eruptive mechanism is believed to occur at a particular stage in root development (Figure 8b).¹⁹
• Type 3: both types of PFE (Types 1 and 2) co-exist in different quadrants on the same patient.¹⁸

Aetiology of PFE

The precise aetiology of PFE is unclear, and there are limited genetic studies in the literature. Ahmad et al found a strong family history of eruption failure, or eruption problems, in the primary dentition. Nevertheless, absence of a family history does not necessarily exclude PFE as the condition can arise de novo, resulting from a spontaneous mutation.¹⁸

Variants in the PTH1R gene, which encodes for parathyroid hormone receptor (PTH1R) and PTH-related peptide (PTHrP) have been identified in patients with PFE.²⁰ Both PTH and PTHrP have essential roles in the developing and remodelling of skeletal tissues by regulating calcium homeostasis and bone metabolism. Both signalling molecules are essential in tooth eruption as they facilitate osteoclast activation, which resorbs bone and facilitates an eruption path for the tooth. PTHrP is involved in physiological root resorption of primary teeth during the eruption of permanent teeth. The postulated mechanism of the PTH1R-mutation leading to PFE is poorly understood; however, it is known that anterior teeth are not affected when mutations with PTH1R are causative.²⁰ Additionally, genetic studies have identified potential causative polymorphisms near the protein coding gene, periostin (POSTN), but the significance of this is unclear.²¹ Genetic testing of the PTH1R gene mutation is a reliable way to confirm a diagnosis; however, this is rarely available in clinical practice.

Primary failure of eruption (PFE) versus mechanical failure of eruption (MFE)

Differentiating between primary failure of eruption (PFE) and mechanical failure of eruption (MFE) is challenging and misdiagnosis is common. MFE has a normal eruption mechanism; however, there is radiographic appearance of relative submergence due to ankylosis (the pathological fusion between the cementum of the tooth and alveolar bone), as opposed to a failure in the tooth's eruption mechanism.

Ankylosis is diagnosed radiographically by the absence of the periodontal ligament space, along with the absence of physiological mobility and a high percussive tone. Assessing the periodontal ligament space radiographically is challenging, particularly if the ankylosis affects the facial/lingual root surfaces, which may not be viewed from the two-dimensional perspective. Accurate diagnosis of ankylosis radiographically can therefore be challenging.

Successful diagnosis often follows a period of close monitoring and observation of the patient's response to treatment.²² Sharma et al²² proposed a protocol to aid the differentiation and diagnosis of PFE and MFE (Table 4).

Management of PFE

The management of PFE depends largely on the severity of the condition and, specifically, whether there is localized or generalized involvement.²² Applying orthodontic forces to these teeth will result in ankylosis and subsequent intrusion of adjacent unaffected teeth. This should, therefore, be avoided.³ If dentists suspect a failure of eruption, they should investigate for local causes, for example odontomes, supernumerary teeth and bony defects from previous surgery. However, if no causes can be identified, children should be referred to specialist paediatric dentistry services as multidisciplinary input is likely to be required for treatment planning.

No intervention

In cases of localized involvement when there are no major aesthetic or functional concerns, no intervention may be recommended. No intervention could however, potentially lead to worsening of the posterior open bite, which may result in functional issues such as masticatory, speech or swallowing difficulties. Patients may also rely on the anterior teeth for mastication, which could result in localized tooth surface loss. If no intervention is the treatment of choice, close clinical follow up is required in all cases.

Removable prosthesis

Some authors have recommend correcting the lateral open bite with a removable prosthesis.²³ This restores the posterior occlusion and maintains the vertical occlusal dimension. The prosthesis should be readjusted according to growth, to allow for maxillary expansion and growth.

Composite build ups and onlays

Composite build ups or onlays can help to restore occlusal stability and preserve alveolar bone level in milder cases, where some tooth eruption has occurred. In these cases, the vertical position of the affected tooth is accepted, and the occlusion is achieved via the restoration. This conservative treatment option allows preservation of the alveolar bone until after pubertal growth, at which point an osseo-integrated dental implant could be considered.²²

Surgical extraction

Surgical extraction of the affected tooth followed by orthodontic space closure or prosthetic replacement may be appropriate in cases with localized involvement.¹⁶ Surgical extractions can, however, be challenging in these cases owing to dilacerated or ‘hooked’ roots, and deep location of the affected teeth, which risks antral communication or damage to the inferior alveolar nerve. Extraction is also likely to result in significant bone loss, necessitating a bone graft prior to prosthetic rehabilitation or implant placement.³

Segmental osteotomy

Severe cases with generalized involvement are more difficult to manage and may be managed with a segmental osteotomy followed by a bone graft or distraction osteogenesis.²⁴ These cases require careful planning to ensure there is no damage to the adjacent teeth. Segmental osteotomy may establish an acceptable occlusion or simply move the teeth into a more favourable position to aid prosthetic replacement.²²

Conclusion

PFE is an uncommon condition characterized by partial or complete failure of a tooth or teeth to erupt.² Diagnosis is usually based on a process of elimination, once all other potential causative factors have been considered and excluded.³ Genetic testing can facilitate a diagnosis; however, this is not routinely available in clinical practice. A comprehensive clinical and radiographic assessment along with a detailed family history must therefore often suffice. PFE is particularly challenging to treat. Applying orthodontic forces to these teeth will be unsuccessful.² Removable overdentures and composite build ups or onlays may be considered to restore occlusal stability. Most commonly, however, no intervention is required. In cases with generalized or multi-quadrant involvement, more radical surgical interventions such as segmental osteotomies and distraction osteogenesis can be considered.